Towers
<p>
Fill in the grid with towers whose heights range from 1 to the grid
size, so that every possible height appears exactly once in each row
and column, and so that each clue around the edge counts the number
of towers that are visible when looking into the grid from that
direction. (Taller towers hide shorter ones behind them. So the
sequence 2,1,4,3,5 would match a clue of 3 on the left, because the
1 is hidden behind the 2 and the 3 is hidden behind the 4. On the
right, it would match a clue of 1 because the 5 hides everything
else.)
<p>
To place a tower, click in a square to select it, then type the
desired height on the keyboard. To erase a tower, click to select a
square and then press Backspace.
<p>
Right-click in a square and then type a number to add or remove the
number as a pencil mark, indicating tower heights that you think
<em>might</em> go in that square.
<p>
Left-click on a clue to mark it as done (grey it out). To unmark a
clue as done, left-click on it again.